Titanium’s difficulty in machining stems primarily from four characteristics: First, its extremely low thermal conductivity, only 1/4 that of steel, concentrates cutting heat at the tool tip, leading to rapid tool wear. Second, it exhibits strong work hardening, resulting in a significant increase in surface hardness after cutting, further exacerbating tool wear. Third, it has high high-temperature chemical reactivity, easily bonding and diffusing with the tool material. Fourth, its low elastic modulus leads to significant springback during cutting, making dimensional accuracy difficult to control. These four characteristics collectively result in low machining efficiency, high tool wear, and demanding process requirements for titanium alloys.

The mainstream choice is fine-grained cemented carbide tools with a TiAlN/AlTiN PVD coating, balancing high-temperature hardness and toughness, making it the most cost-effective option. For finishing or high-requirement applications, PCD diamond-coated tools can be used. These tools have a lifespan 3-5 times longer than ordinary coated tools, but are more expensive. High-speed steel tools are only suitable for low-speed machining of pure titanium and are not recommended for alloy titanium. For tool geometry, a large rake angle and large helix angle are preferred to reduce cutting forces.

Standard tolerances for conventional titanium parts can be consistently achieved at ±0.1mm. Precision machining can achieve ±0.02-0.05mm. High-precision CNC machining centers can reach a limit of ±0.005mm. Specific tolerance capabilities depend on the part’s size, structure, and feature type. For example, tolerances for thin-walled parts and deep holes will be correspondingly more lenient. Tighter tolerances result in higher machining costs; it is recommended to only specify tight tolerances for critical features.

Main reasons for titanium deformation: low elastic modulus, high residual cutting stress, and high thermal sensitivity. Core solutions to prevent deformation: ① Use symmetrical structures, uniform wall thickness, and added reinforcing ribs during the design phase; ② Perform stress-relief annealing after rough machining to release cutting stress; ③ Employ symmetrical layered cutting and shallow depth-of-cut multi-path processes; ④ Use multi-point flexible tooling for uniform clamping to avoid localized deformation; ⑤ Perform precision machining in a constant-temperature environment to control thermal deformation.

There are four main reasons for the high cost: ① Expensive raw materials: Titanium alloy bars are 10-20 times more expensive than aluminum alloys; ② Low machining efficiency: Cutting speed is only 1/5-1/8 that of aluminum alloys, resulting in high per-piece machining costs; ③ High tool wear: Specialized tools are expensive and wear out quickly, with tool costs 3-5 times that of aluminum alloys; ④ High quality control costs: Industries such as aerospace and medical require strict testing and traceability, adding extra costs.

Grade 5 (Ti-6Al-4V) is significantly more difficult to machine than Grade 2 pure titanium. Grade 5 (Ti-6Al-4V) has higher strength, greater cutting forces, more severe work hardening, and poorer thermal conductivity, resulting in faster tool wear. Under the same conditions, the cutting speed of Grade 5 is 30%-40% lower than that of Grade 2, the tool life is about 60% of that of Grade 2, and the overall machining cost is 30%-50% higher. Grade 5 is not recommended for applications where Grade 2 can meet the requirements.

Titanium alloys are very suitable for anodizing, which is the most common surface treatment for titanium. Electrochemical oxidation creates a dense titanium dioxide film on the surface, with benefits including: ① significantly improved corrosion resistance; ② increased surface hardness and wear resistance, reducing seizing; ③ the ability to produce various colors such as gold, blue, purple, and green for marking and decoration; ④ an extremely thin film that hardly affects dimensional accuracy. It is widely used in aerospace fasteners, medical devices, and exterior parts.

Grade 23 is a Ti-6Al-4V ELI (ultra-low interstitial element) version. The content of impurities such as oxygen, nitrogen, and iron is significantly lower than that of ordinary Grade 5. Compared to Grade 5, it has higher fracture toughness and better resistance to fatigue crack propagation, making it safer and more reliable under alternating loads after implantation. The lower impurity content also improves biocompatibility and reduces the risk of tissue reaction. Grade 23 meets the ASTM F136 standard for medical implants and is the preferred material for orthopedic and dental implants.

Titanium can be welded, commonly using techniques such as TIG welding and plasma welding. However, the welding requirements are very strict. Key points to note: ① Welding must be performed under high-purity argon gas protection, both sides must be protected to prevent air, hydrogen, oxygen, and nitrogen from entering the weld and causing embrittlement; ② Thoroughly clean the weld area of ​​oil and oxide scale before welding to avoid contamination; ③ Stress-relief annealing is recommended after welding to eliminate welding stress; ④ Critical welds must undergo non-destructive testing to verify the absence of porosity and cracks.

Three common verification methods: ① Density method: Titanium has a density of 4.51 g/cm³, which is about 40% lighter than stainless steel, making it significantly lighter for the same volume; ② Spectroscopic detection: XRF spectrometers can quickly detect elemental composition and accurately determine the grade, making it the most commonly used on-site testing method; ③ Hardness test: Different grades of titanium alloys have distinct hardness ranges, which can assist in verification. Reputable suppliers will provide original factory material certificates. Wstitanium conducts spectral re-inspection on every batch of materials entering the factory.

Titanium surface treatments include: ① Anodizing: the most mainstream method, improving corrosion and wear resistance, and allowing for coloring; ② Sandblasting: achieving a matte surface, used as a pretreatment for coatings; ③ Grinding/Electropolishing: achieving a high-gloss surface, used in seals and medical components; ④ PVD Coating: an ultra-hard coating, significantly improving wear resistance; ⑤ Powder Coating/Electrophoresis: for corrosion protection and surface finishing.

For CNC machining of thin-walled titanium alloys, a minimum thickness of ≥1mm is recommended to ensure stable tolerances and flatness. With structural reinforcement, 0.8mm is possible. Under extreme conditions, non-load-bearing decorative parts can achieve 0.5mm, but this carries a high risk of deformation and significantly increases costs. The thinner the wall and the greater the height, the more difficult the machining becomes. It is recommended to control the height-to-thickness ratio to within 5:1 during the design phase.

Titanium can be threaded through turning, milling, and tapping. Metric thread precision can consistently reach 6H/6g level, and precision machining can achieve 5H/5g level. Tapping titanium is more difficult; for fine and deep threads, thread milling is recommended for better chip removal, more stable precision, and lower risk of tool breakage. Coarse threads should be prioritized in the design phase to reduce machining difficulty and cost.

Selection principle: Choose the grade with the lowest cost and easiest processing while meeting performance requirements.
① For only corrosion resistance and no high load: Choose Grade 2 pure titanium, the lowest cost and easiest processing;
② For medium strength and cold forming: Choose Grade 9;
③ For high-strength structural components and high-temperature use: Choose Grade 5;
④ For medical implants: Choose Grade 23;
⑤ For highly corrosive environments and crevice corrosion environments: Choose Grade 12 or Grade 7;
⑥ For high-temperature creep requirements: Choose Grade 6.

Ordinary milling achieves Ra 1.6-3.2μm; finish milling can reach Ra 0.8-1.6μm; finish turning can reach Ra 0.4-0.8μm; grinding can reach Ra 0.1-0.4μm; electropolishing can achieve a mirror finish with Ra 0.02-0.2μm. Higher surface roughness requirements result in higher processing costs.